What is MEF2C haploinsufficiency syndrome?

MEF2C haploinsufficiency syndrome is a genetic condition which affects body development and particularly brain development. The condition is also known as ‘mental retardation, autosomal dominant 20’ or ‘chromosome 5q14.3 deletion’ syndrome.

The first patients with MEF2C haploinsufficiency syndrome were described in 2009. People with MEF2C haploinsufficiency syndrome have variable degrees of developmental delay, hypotonia, seizures, stereotypic movements and characteristic (though subtle) facial features.

Genes are instructions which have important roles in our growth and development. They include all the information to construct a human body as the colour of the eyes and a normally functioning brain. They are made of DNA and are incorporated along with many other genes into organised structures called chromosomes. Each person has several thousand genes in two copies, one copy inherited from his dad and one copy inherited from his mum.

MEF2C haploinsufficiency syndrome is caused by pathogenic variants (point mutations or deletions) of the MEF2C gene which is located on chromosome 5 in band 5q14.3. MEF2C pathogenic variants occur out of the blue (de novo) and affect boys and girls in the same way. To the best of our knowledge, all the affected people are the first person in their family to have the pathogenic gene variant. However, this is a disorder with “autosomal dominant” inheritance which means that if individuals with a MEF2C pathogenic variant has children, they have a 50% chance of having an affected child.

For specific advice about the chance of this happening again, it would be sensible to speak to a clinical geneticist or genetic counsellor.

How common is MEF2C haploinsufficiency syndrome?

Pathogenic variants in MEF2C gene are rare. Sixty individuals have been reported in the medical literature, so far (2017). It is likely, however, that there are still undiagnosed individuals.